1. Technical Field
The present invention relates to a secondary battery, and more particularly, to a secondary battery having an electrode assembly which can prevent an internal short circuit.
2. Related Art
Various batteries are used as power sources for electric appliances, and particularly, lithium secondary batteries are widely used as power sources for compact electric appliances because they can realize high capacity with small volume, they have a high energy density per unit area, and they are rechargeable.
Lithium secondary batteries are formed by accommodating an electrode assembly, which is formed by stacking and winding positive and negative electrode plates formed by applying active materials to positive and negative electrode collectors, respectively. A separator is disposed between both electrode plates, and an electrolyte is injected into a cell case and the cell case is sealed.
Lithium secondary batteries may be classified into a cylindrical type, a rectangular type and a pouch type, depending on the shape of the cell case.
Generally, to accommodate the electrode assembly in the cell case, the electrode assembly is wound, and then surrounded by tape to hold the electrode assembly is a wound state.
That is, the tape laterally surrounds the electrode assembly which is formed by winding the positive electrode, the separator and the negative electrode to cover an end of the wound electrode assembly.
In this respect, the completely wound electrode assembly is held by tape attached to the positive electrode plate, i.e., an outermost layer.
Accordingly, when the separator formed of resin is contracted in a lateral direction of the electrode assembly, which is the vertical direction, due to charge or discharge of the battery, or thermal impact, the positive and negative electrode plates are in contact with each other in an empty space formed by the contraction of the separator, causing an electrical short circuit to occur.
Particularly, the electrode assembly is severely exposed to heat and is heated at upper and lower parts so that the contraction of the separator can be easily generated at upper and lower parts of its end.